Changelog:

• ZipFS can now generate zip indexes responsively. See sample code below.
• OverlayFS and AsyncMirror throw exceptions if a program uses them before initializing them.
• IE9 compatibility fix. Under particular circumstances, BrowserFS would trigger a Uint8Array not defined. exception

The ZipFS change lets you generate a zip file's index prior to creating the file system:

ZipFS.computeIndex(zipAsBuffer, function(index) {
  var zfs = new ZipFS(index);
});

The older new ZipFS(zipAsBuffer) signature continues to work, as well, but that will synchronously populate the zip index.

Credit goes to @hrj for this contribution!